[T3304] FIX: lazy-load letter previews, reveal shell on DOMContentLoaded

[Danielgergely]

• FIX: reduces loading time of the letter page

[greptile-apps]

Confidence Score: 5/5

The updated letter-preview and Capacitor visibility behavior is safe to merge based on the exercised browser and DOM interactions.

No defects remain. The changed lazy-loading, already-read click, and Capacitor reveal paths were executed successfully.

Files Needing Attention: No files need follow-up attention.

T-Rex Logs

What T-Rex did

• Ran focused jsdom and headless Chromium validations against the changed letter-preview JavaScript, letter-card markup and styling, and Capacitor visibility script.
• Verified the read-letter iframe size inside the envelope (90.71 × 15 px) and confirmed data-src promotion to src when entering the configured 300 px root margin, and that clicking an already-read envelope navigates to the PDF URL through the standard interaction path.
• Confirmed normal DOMContentLoaded handling and a late-listener simulation that restores document opacity to 1.
• Validated that iframe observability remained functional and the already-read click navigated to the intended PDF URL; observed normal DOMContentLoaded and timeout fallback, and noted that an authored runnable test source and its captured output were uploaded.

_{Ran code and verified through T-Rex}

_{Reviews (1): Last reviewed commit: "[T3304] FIX: lazy-load letter previews, ..." | Re-trigger Greptile}